DuPont Delrin selection question

[awparran]

About a month ago I asked for information on replacing nylon or Teflon with a more modern polymer product. It was suggested that I look at the properties of Dupont's Delrin.

Since then I have had the oportunity to look at the spec data, and have come up with a few questions.

The Delrin 570 has better mechanical properties than the 150 SA. My question is, should I just use the 150? Do I need anything as exotic as the 570?

I am only going to use the Delrin as a very, very low speed bearing. Each one will be approx. 2" dia. X 2.5" in length.

I am looking for good lubrication and thermal properties. Due to the short section lengths, stiffnes should not requirement or problem.

Or since all of the products are so low in cost should I just go for the added safety????

Tony

 

[MikeHalloran]

You haven't described your application.

Safety? As in aircraft parts?

Radial load? Loading time spectrum?

Mating surface? Environment?



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[awparran]

The parts are to be used in my Flaperon Mixer design.

The Delrin will serve as bearings between two rotating tubes. Since the rotation is based on pilot contorl input, i.e., left or right bank, flaps up or down, there is very little rotational speeds, but might encounter some heavy loads causing deformation.

My design calls for a 0.5" center support (This might be overdesigned, but I was looking for support rather than strength here.) The center bearing will fit inside this support, whereas the outer bearings will serve as end caps, backed up by a .125" 4130 plate.

So if you can imagine: a flat plate, an endcap, a tube, a bearing supported by a support bracket, another tube, another endcap, and another flat plate. Each tube is independent of the other. As the pilot induces an input, there is sure to be some form of aerodynamic resistance causing a load on the bearings surface.

The tubes are 4130 2.0" O.D. with a wall thickness of 1/16" The Delrin would be machined to fit inside the tubes to a depth of .75" with a lip for the end caps of .25" X 2.25" O.D. The center bearing would have a support lip of 1", and both sides extending into the tubes of .75".

So my question is will the Delrin 150 SA be capable of taking such loads or should I use the 570, or scrap my idea and use another material, again the idea is for self-lubrication, and ease of maintenance.

Thanks in advance for your time.

Tony

 

[Sparweb]

How about testing some samples? Perhaps you project only requires a small quantity of bushing material to begin with, but by trying some experiments sounds like the only way you will satisfy yourself.
My mental picture is of two tubes, one inside the other, with the bushing material keeping them apart. You previous post didn't describe the loads on the system, so one can only guess if loads are even a factor. Probably more important are wear, temperature extremes, and contamination and how they affect the freedom of motion over time.


Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[awparran]

Hi SparWeb:

Yes, I was going to do that. I had hoped someone already had experience with it.

I will have to look up on the Internet and run some examlpes of a life-cycle testing program.

Thanks

Tony

 

[awparran]

I have finished 90% of the drawings for the flaperon controls, including the flap handle. I might even build a scale model.

 

[WKTaylor]

tparran...

We recently noted a problem with flight control bearings that You need to be aware of. Plain bearings [IE: self lubricated bearings, such as metal bushings with PTFE liners] with precision fit [for minimal/no back-lash/freeplay] tend to have high "break-away" friction co-efficents. Wide temperature variations can aggravate this problem. Add environmental factors such as dust, moisture, incidental fluid contact, ice, etc... and friction forces can become VERY high. What is normally a "smooth/low-friction system" under ideal conditions, could in-fact become very "stiff/sticky" under real-world conditions.

There are several PRECISION self-lubricated plain bearings made per MSxxxxx [now ASxxxxx] specs... and several proprietary bearing manufacturers, such as KAMATICS that make bearings with styles similar to the MS/AS parts... with claims of dimensional stability, low/no break-away friction, long life, chemical resistance, etc.

Note: some mfgrs will actually apply [bond] their proprietary non-metallic self lubricating [hybrid-plastic] materials to surfaces of OEM parts and precision grind/machine to match drawing requirements. This means that You could be free-to-design to an arbritrary configuration... with the bearing material integral to one, or multiple, parts.

Regards, Wil Taylor